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Less grays: more readable palette since usually we have a non linear
distribution of percentages and very near gray tones are hard to take
apart. Final part of the palette is gradient from yellow to red. The red
part is hardly reached because of usual distribution of latencies, but
shows up mainly when latencies are very high because of the logarithmic
scale, this is coherent to what people expect: red = bad.

Unify to uppercase the headline

Related to PR #2357.

Support "1G" etc. units in CONFIG SET maxmemory

Related to PR #2357.

The old version of SPOP with "count" argument used an API call of dict.c
which was actually designed for a different goal, and was not capable of
good distribution. We follow a different three-cases approach optimized
for different ratiion between sets and requested number of elements.

The implementation is simpler and allowed the removal of a large amount
of code.

Now the API automatically creates its argv copy and increment ref count
of passed objects.

Severan problems are addressed but still a few missing.
Since replication of this command was more complex than others since it
needs to replicate multiple SREM commands, an old API able to do this
was reused (it was taken inside the implementation since it was pretty
obvious soon or later that would be useful). The API was improved a bit
so that now a command may opt-out for the standard command replication
when the server.dirty counter is incremented, in order to "manually"
replicate what it wants.

Fixed by @oranagra, thank you.

Avoid code repetition introduced with PR #2367, also fixes the return
value to always return 0 if there is nothing more to rehash.

This is very similar to the optimization applied to dictGetRandomKeys,
but applied to the single key variant.

Related to issue #2306.

Related to issue #2306.

We use the invariant that the original table ht[0] is never populated up
to the index before the current rehashing index.

Related to issue #2306.

Related to issue #2306.

Related to issue #2306.

Related to issue #2306.

This test on Linux was extremely slow, since in Tcl we can't enable
easily tcp-nodelay, so the busy loop used to take *a lot* with bigger
writes. Fixed using pipelining.

Related to issue #2372.

Fix HAVE_BACKTRACE on Linux

--stat mode already used to reconnect automatically if the server is no
longer available. This is useful since this is an interactive mode used
for debugging, however the same applies to --latency and --latency-dist
modes, so now both use the reconnecting command execution as well.

The reconnection code was modified to use basic VT100 escape sequences
in order to play better with different kinds of output on the screen
when the reconnection happens, and to hide the reconnection attempt
output when finally the reconnection happens.